Flameroofing of wood and article



2,990,297 FLAMEPROOFING W091!) AND ARTICLE Charles M. Shaw, Albany, Calif, assignor to California Research Corporation, San Francisco, Calif., a corporation of Delaware N0 Drawing. Filed Dec. 21, 1959, Ser. No. 860,633 4 Claims. (Cl. 117-137) This invention relates to the production of flameproof articles of superior quality. More particularly, the invention is concerned with improved production of articles of wood possessing excellent fire-resisting properties by treatment with compositions containing thiophosphorus compounds and unique combinations thereof.

Wood is employed extensively in many present day structures because it is often more available and easier to work with on location than other materials. Bridges, telephone poles, railroad trestles, loading docks and marine wharves are illustrative of some of the more common uses. In such applications, it is generally desirable to treat the Wood with preservative oils to prevent decay or other deterioration. Unfortunately, the treated Wood structures are even more susceptible to damage by fire because of the flammable nature of the preservative oil which is cumulative to the normal combustibility of the wood.

Fire damage is also a matter of concern in many im flammable articles other than wooden structures. For example, cotton and similar fibers used in the manufacture of cloth such as canvas for tents and tarpaulins are well known for their flammability. Such articles also are commonly treated with preservatives which add to the normally flammable character of the fibers.

It has now been found that wood is effectively flameproofed by treating with a superior new composition comprising a major proportion of liquid vehicle, more particularly a wood preservative oil, and at least by weight of a member of the groups consisting of (1) reaction product of phosphorus pentasulfide and pinene, (2) zinc dialkyl dithiophosphate containing from 3 to 8 carbon atoms in each of the alkyl groups and zinc dialkylphenyl dithiophosphate containing from 14 to 24 carbon atoms in each of the alkylphenyl groups, and (3) combination of members of each of group (1) and group (2), said combination consisting of from to 90% by weight of reaction product and from 10 to 90% by Weight of zinc dithiophosphate.

The normally inflammable nature of Wood or other such flammable articles is remarkably inhibited by treatment with the flameproofing compositions of this invention. The unique combination of thiophosphorus compounds in the compositions in particular provides a much greater fire retarding effect than would be expected from the performance of either one of the thiophosphorus compounds alone.

The term flameproof is used in this description in its commonly accepted sense and refers to the treatment of the article so that it is resistant to the propagation of flame once the ignition source has been removed. This use is consistent with the definition of the term in the ASTM standards yearbook for 1944 under Test D626-41T.

The liquid vehicles and preservative oils of the compositions according to this invention are primarily for the purpose of providing a suitable carrier for applying the thiophosphorus composition to the article being treated. Aqueous compositions are useful. Preferably, however, the liquid vehicle is an oil. The oil may be designed to evaporate and leave the fiameproof composition of the phosphorus compounds as a residue in the treated article, as in the case of a light thinner or petroleum naphtha. It may be designed to penetrate and serve as a preservaice five or it may remain largely on the surface and serve as a finish or protective coat. For example, linseed or other vegetable oils and natural or synthetic resins may be used to form flameproof coatings. Various petroleum and coal tar derived oils, such as cresols,

aromatic petroleum extracts, medium boiling fuels of the diesel oil and furnace oil type, and heavier fuels, for

example, topped naphthenic crude oil may be used to penetrate and preserve the article treated. The wood preservative oils having pesticidal and fungicidal properties such as creosote and petroleum hydrocarbons containing pentachlorophenol, and combinations thereof, are presently preferred.

The reaction product of phosphorus sulfide and pinene is the material resulting from the condensation of a terpene such as present in turpentine with a phosphorus sulfide such as phosphorus pentasulfide. In the preparation of these condensation pro-ducts, the ratio of turpentine to phosphor-us pentasulfide is usually within the range of about 1:1 to about 3:1. The condensation is exothermic and proceeds spontaneously after heating slightly to initiate the reaction. Usually, the turpentine or other pinene or terpene containing material is heated to about 200 F. and the phosphorus pentasulfide is added slowly with stirring. Cooling may be employed if necessary to avoid undesirably high temperatures in excess of 300 F. In the process, addition agents such as aliphatic alcohols, for example, lauryl alcohol may be combined with the turpentine and phosphorus pentasulfide.

Illustrative thiophosphate compounds for present purposes include the metal salts of thiophosphates prepared by the reaction of phosphorus pentasulfide with an aliphatic alcohol or an alkyl phenol. Such reactions are straightforward and excess unreacted materials are readily removed by conventional separation methods, for example, filtration, distillation and the like. The alcohols and phenols, or mixtures thereof, are usually reacted with phosphorus pentasulfide at temperatures of from about 200 to 300 F. The suitable aliphatic alcohols contain from 1 to 16 carbon atoms and preferably 3 to 8 carbon atoms. The alkyl phenols contain from 8 to 24 carbon atoms and preferably 14 to 24 carbon atoms. The dialkyl dithiophosphates formed from the aliphatic alcohols are preferred over the alkyl phenyl analogs from the standpoint of effectiveness and economy of raw materials. The metal salt desired of the phosphorus sulfide reaction product is conveniently formed by the addition of the corresponding metal oxide to the reaction product. The zinc salts are preferred. No special conditions are required, although heating and stirring are usually employed to effect complete reaction.

The pinene-phosphorus sulfide reaction products and the metal dithiophosphates of the flameproofing compositions, as mentioned above, are generally known as lubricating oil additives. They are described in considerable detail in various texts on lubricating oil additives. A brief description of such additives is to be found at pages 167 and 178 of Motor Oils and Engine Lubrication by Georgi, published in 1950 by Reinhold Publishing Corporation, New York, New York. So far as is known, such compounds have not been suggested in the form of the present compositions and concentrates, nor have they been proposed for use with wood preservative oils as flameproofing compositions.

The combination of phosphor-us pentasulfide and pinene reaction product and the zinc dithiophosphate, as mentioned above, is surprisingly effective. It may vary in proportions so long as there is at least 10% by weight of each of the compounds in the combination. For present purposes, the combination of thiophosphorus compounds satisfactorily ranges from 10% to byweight of the combination as phosphorus pentasulfide pinene reaction product and 10 to 90% by weight as zinc dithiophosphate. 'Ordinarily, maximum benefit of the combination of additives is obtained with 40 to 60% by weight of each in the combination.

The phosphorus pentasulfide-pinene reaction product,

. the zinc dithiophosphate and the combination thereof in the preservative oil are used in minor proportions sufficient to inhibit or retard burning of the final treated article. At least 5% by weight of the compounds or combination on the basis of total composition is ordinarily desirable, particularly in the treatment of wood. Usually not more than 20 or 30% of the thiophosphate compounds is required for effective fiameproofing.

For present purposes, the impregnation of the wood is preferably carried out in conjunction with a wood preservat'ive treatment employing the compositions and treating processes as described above. The liquid vehicle or preservative oil of the compositions employed in the production of flameproof wood according to this invention is so selected so that it dissolves the thiophosphorus compounds in the concentrations mentioned above. The thiophosphorus compounds themselves are retained on and in the treated wood in amounts suificient to provide the desired fire resistance. Such amounts may vary considerably. Usually about one pound of the thiophosphorus compounds per cubic foot of wood is sufiicient to provide greatly improved fire retarding properties. The wood is treated satisfactorily according to the present method by the use of conventional processes such as by simple soaking. The full cell pressure process and empty cell process commonly used in the impregnation of wood are also satisfactory.

The following compositions are illustrative of those employed in the production of flameproof wood according to the invention:

The standard crib burning tests show the effect of the flameproofing compositions on a field scale. In the crib tests, the treated timber being evaluated is arranged in the form of a square crib. The timber is cut from thoroughly air-seasoned 7 in. x 9 in. x. 8 ft. Douglas fir cross ties having a moisture content of 11 to 13%. The ties are cut into six pieces of three sizes: 4% in. x 7 in. x 8 ft. rough, 4 in. x 4 in. X 24 in. smooth on four sides, and Z in. X4 in. x 2 in. smooth on four sides. The number of pieces of each size treated with the flameproofer is approximately double the number used. The pieces with the highest and the lowest retentions are rejected. The 4% in. x 7 in. pieces are treated in the original 8 ft. length. Before testing, 8 inches is cut off the ends of each piece and the remainder is cut in half. Thus, the pieces actually burned are 4 /2 in. x 7 in. x in. The 2 x 4 and 4 x 4 pieces are treated and burned in the 24 in. length.

In these tests, a comparison is made by the use of four difierent treatments. The treatments are: (1) straight creosote; (2) an aqueous solution containing about 8% of water soluble salts consisting of 10% diammonium phosphate, ammonium sulfate, 20% sodium tetraborate anhydrous and 10% boric acid; (3) a commercially available flameproofing composition consisting of 88% creosote and 12% tricresylarylphosphate (8.6% phosphorus); and (4) a composition according to the present invention consisting of 10% by weight of the concentrate of Example 1 and 90% by weight creosote.

The cribs are set up as hollow squares approximately 4 ft. high. The cribs of the 4% in. x 7 in. x 40 in. pieces are open on top while the cribs of the 4 x 4 and 2 x 4s are closed on top. The ignition is by means of a gasoline fire. In the testing of the 4 /2 x 7 pieces an aluminum pieplate with /2 pt. of gasoline is set in the center of each crib and the 2 cribs tested together are ignited at the same TABLE I Composition Carrier or typed Pre- Percent Compound (1) Percent Compound (2) Percent serve We {Diesel Fuel Oil 90. 0 Zinc ditetradeeyl-phenyl di- 4. 25 Turpentine P'lss Reaction 4. 25

Pentachlorophenol l. 5 thiophosphate. Product. Oreosotc 90.0 Z1110 butyl hexyl dithio- 1.0 Pincus-P285 Reaction 9.0

phosphate. Pro u Grade 1 N aphthenic 85.0 inc didodecyl dithlophos 10.0 do 5. 0 E 1 1 90 o z' ii' t 1 1 arm iese u me u y amy 1o- \Pentachlorophenol 5.0 phosphate. Creosote 80.0 Zinc dodecylphenyl hexyl 18.0 Turpentine-PzssReaction 2.0

dithwphosphate. Product. No. ZFurnace Oil. 95.0 Zinc methyl ethyl dithio- 2.0 Pincus-P285 Reaction 3.0

phosphate. Product. Water 85. 0 Zine ditetradecyl-phenyl di- 5. 0 TurpentinePzSi Reaction 5. 0

thiophosphate. Product. Creosote 90.0 Zinc butyl amyl dithio- 10.0

. phosphate. do 90.0 Pinene-PZSS Reaction 10.0

4 Product. Boiled Linseed 011-... 90.0 Zinc butyl amyl dlthio- 5.0 do 5.0

phosphate.

The efiectiveness of the flameproofing treatment according to the present invention is further illustrated by the following examples. In these examples, the proportions, unless otherwise specified, are given on a Weight basis:

Example I of a medium boiling liquid aromatic petroleum hydro-' carbon S0 extract. Treatment with the flameproofing composition thus prepared is found to give excellent fire V retarding properties to wood in the standard tests, as

describedbelow. V

time. In the 4 x 4 cribs, the gasoline is held in 1 qt. cans for about 2 minutes, at which time the cans are tipped over to ignite the wood. Temperatures reached in the fire are measured and go as high as about 2,000 F. after about 10 minutes down to about 200 F. after 40 minutes of burning time. In the tests, the time for the fire to go out is measured, as well as the time for any collapse of the timbers. The weight of the remainders of the pieces after scraping ofi char is also measured.

The results of the tests are given in the following table.

Set No. 1--4- A" x 7" x 40" pieces Collapsed 104. Out in 45. Out in 45. Out in 33.

Set No. 2 x 4" x 24" pieces Collapsed. Out in 34. Out in 29.

Collapsed 35. Collapsed 48. Collapsed 66.

Very small flames remained at ends of a few places.

It is readily seen from the above test results that the flameproofing treatment of this invention is remarkably more effective than treatment with commercial compositions presently in use. The need for treatment with flameproofing compositions is clearly shown in the test results. Wood treated with preservative oil alone such as the creosote is completely consumed in the test. Employing the flameproofing treatment of this invention, it is seen'that a substantial amount of the flameproofer is retained by the treated wood, there is less weight lost in the wood and the flames burn themselves out and the fire is self-extinguished in a shorter period of time. Thus, in each of the three critical evaluations of the effectiveness of typical flameproofing agents, the flameproofing treatment according to the invention is found to be superior.

Example [I In this example, the widely-accepted Panel Fire Test is employed to evaluate the flameproofing treatment and flameproof articles of wood of this invention. In the tests, treatment with flameproofing compositions employing the two difierent thiophosphorus compounds separately and in combination are carried out to show the effectiveness of the treatment. The improvement obtained when the thiophosphorus compounds are employed in combination in accordance with a preferred embodiment of the present invention is also shown.

Douglas fir panels are made up of three pieces of 2 in. x in. x 14 ft. long wood and two pieces of 2 in. x 6 in. x 14 ft. long. The panels are treated under the usual temperature and pressure conditions with 10% by weight of each flameproofing agent in a 50:50 percent by weight mixture of creosote and residual fuel oil (topped naphthenic crude). The panels are allowed to weather for a period of at least 60 days. Following this, the panels are installed as part of the flooring in a mock-up railroad trestle section. The burning of the panels is accomplished by the ignition of tumbleweed stacked tightly under the trestle section. During the burning, temperatures between about 1500 F. and 1600 F. are reached.

The following table shows the results of the tests. In Composition No. 1, the flameproofing agent added to the 50:50 creosote and residual fuel is 85% by weight alphapinene and phosphorus pentasulfide reaction product in combination with 15% by weight of medium boiling petroleum aromatic hydrocarbon extract. The agent of Composition No. 2 is 85% by weight zinc butyl hexyl dithiophosphate and 15% extract. Composition No. 3 uses a typical concentrate consisting of 42.5% by weight alpha-pinene and phosphorus pentasulfide reaction product, 42.5 by weight zinc butyl hexyl dithiophosphate and 15% by weight aromatic hydrocarbon extract.

The above test results show conclusively that remarkable flameproof properties are obtained by treatment with the composition according to the process of this invention. It will also be seen from the above test results that treatment with Composition No. 3, in particular, containing the combination of thiophosphorus compounds in accordance with the invention is superior to treatment with Compositions 1 and 2 containing the single thiophosphorus compounds. Considerably more of Composition 3 is retained in the wood compared to Compositions 1 and 2. The burning time is definitely shorter and the weight loss of the wood due to burning is approximately 30% less than the best of the other two compositions, namely Composition No. 2.

I claim:

1. A fiameproofed article of wood, said wood being impregnated with a flameproofing amount of a composition comprising a major proportion of a wood preservative oil and at least 5% by weight of a member of the groups consisting of (1) reaction product of phosphorus pentasulfide and pinene, (2) zinc dialkyl dithiophosphate containing from 3 to 8 carbon atoms in each of the alkyl groups and zinc dialkylphenyl dithiophosphate containing from 14 to 24 carbon atoms in each of the alkylphenyl groups, and (3) combination of members of each of group (1) and group (2), said combination consisting of from 10 to by weight of reaction product and from 10 to 90% by weight of zinc dithiophosphate.

2. A method of fiameproofing Wood which comprises impregnating said wood with a flameproofing amount of a composition comprising a major proportion of a wood preservative oil and at least 5% by weight of a member of the groups consisting of (1) reaction product of phosphorus pentasulfide and pinene and (2) 'zinc dialkyl dithiophosphate containing from 3 to 8 carbon atoms in each of the alkyl groups and zinc dialkylphenyl dithiophosphate containing from 14 to 24 carbon atoms in each of the alkylphenyl groups, and (3) combination of member of each of group (1) and group (2), said combination consisting of from 10 to 90% by weight of reaction product and from 10 to 90% by weight of zinc dithiophosphate.

3. A method of flameproofing wood which comprises impregnating said wood with a flameproofing amount of a composition comprising a major proportion of a 50:50 weight percent mixture of creosote and residual fuel oil and at least 5% by weight of the combination of 1) reaction product of phosphorus pentasulfide and pinene and (2) zinc dithiophosphate selected from the group consisting of zinc dialkyl dithiophosphate containing from 3 to 8 carbon atoms in each of the alkyl groups and zinc dialkylphenyl dithiophosphate containing from 14 to 24 carbon atoms in each ofthe alkylphenyl groups, said combination consisting of from 10 to 90% by weight of reaction product and from 10 to 90% by weight of zinc dithiophosphate.

4. A method of flameproofing wood which comprises impregnating said wood with a flameproofing amount of a major proportion of wood preservative oil and at least 5% by weight of zinc butyl amyl dithiophosphate.

(References on following page) 

1. A FLAMEPROOFED ARTICLE OF WOOD, SAID WOOD BEING IMPREGNATED WITH A FLAMEPROOFING AMOUNT OF A COMPOSITION COMPRISING A MAJOR PROPORTION OF A WOOD PRESERVATIVE OIL AND AT LEAST 5% BY WEIGHT OF A MEMBER OF THE GROUPS CONSISTING OF (1) REACTION PRODUCT OF PHOSPHORUS PENTASULFIDE AND PINENE, (2) ZINC DIALKYL DITHIOPHOSPHATE CONTAINING FROM 3 TO 8 CARBON ATOMS IN EACH OF THE ALKYL GROUPS AND ZINC DIALKYLPHENYL DITHIOPHOSPHATE CONTAINING FROM 14 TO 24 CARBON ATOMS IN EACH OF THE ALKYLPHENYL GROUPS, AND (3) COMBINATION OF MEMBERS OF EACH OF GROUP (1) AND GROUP (2), SAID COMBINATION CONSISTING OF FROM 10 TO 90% BY WEIGHT OF REACTION PRODUCT AND FROM 10 TO 90% BY WEIGHT OF ZINC DITHIOPHOSPHATE. 